<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      body {
        margin: 0;
        height: 100vh;
        display: flex;
        justify-content: center;
        align-items: center;
        background-color: #000;
      }
      form {
        width: 400px;
        height: 100px;
        background: linear-gradient(270deg, transparent, #03e9f4);
        border-radius: 10px;
        display: flex;
        flex-direction: column;
        align-items: center;
        padding: 50px 0;
      }
      #username {
        padding: 10px 15px;
        outline: none;
        border: none;
        /* border-color: #03e9f4; */
        background-color: transparent;
        border-radius: 5px;
        margin-bottom: 20px;
      }
      #entry {
        position: relative;
        display: flex;
        align-items: center;
        text-align: center;
        padding: 25px 30px; 
        color: #03e9f4;
        text-decoration: none;
        text-transform: uppercase;
        transition: 0.5s;
        letter-spacing: 4px;
        border-radius: 4px;
        overflow: hidden;
      }
      a span {
        position: absolute;
        display: block;
      }
      #entry:hover {
        background: #03e9f4;
        color: #050801;
        box-shadow: 0 0 5px #03e9f4, 0 0 25px #03e9f4, 0 0 50px #03e9f4,
          0 0 200px #03e9f4;
        -webkit-box-reflect: below 1px linear-gradient(transparent, #0005);
      }
      a span:nth-child(1) {
        top: 0;
        left: 0;
        width: 100%;
        height: 2px;
        background: linear-gradient(90deg, transparent, #03e9f4);
        animation: animate1 1s linear infinite;
      }
      @keyframes animate1 {
        0% {
          left: -100%;
        }
        50%,
        100% {
          left: 100%;
        }
      }
      a span:nth-child(2) {
        top: -100%;
        right: 0;
        width: 2px;
        height: 100%;
        background: linear-gradient(180deg, transparent, #03e9f4);
        animation: animate2 1s linear infinite;
        animation-delay: 0.25s;
      }
      @keyframes animate2 {
        0% {
          top: -100%;
        }
        50%,
        100% {
          top: 100%;
        }
      }
      a span:nth-child(3) {
        bottom: 0;
        right: 0;
        width: 100%;
        height: 2px;
        background: linear-gradient(270deg, transparent, #03e9f4);
        animation: animate3 1s linear infinite;
        animation-delay: 0.5s;
      }
      @keyframes animate3 {
        0% {
          right: -100%;
        }
        50%,
        100% {
          right: 100%;
        }
      }

      a span:nth-child(4) {
        bottom: -100%;
        left: 0;
        width: 2px;
        height: 100%;
        background: linear-gradient(360deg, transparent, #03e9f4);
        animation: animate4 1s linear infinite;
        animation-delay: 0.75s;
      }
      @keyframes animate4 {
        0% {
          bottom: -100%;
        }
        50%,
        100% {
          bottom: 100%;
        }
      }
    </style>
  </head>
  <body>
    <form>
      <input type="text" placeholder="请输入用户名" id="username" />
      <a href="index.html" id="entry">
        <span></span>
        <span></span>
        <span></span>
        <span></span>
        join
      </a>
    </form>
  </body>
  <script src="./entry.js"></script>
</html>
